Flexible polyurethane foams are well recognized articles of commerce. Flexible polyurethane foams are used in a wide variety of applications, ranging from cushioning (such as mattresses, pillows and seat cushions) to packaging to thermal insulation. Polyurethane foams are typically prepared by the reaction of a polyol component with an isocyanate, in the presence of a blowing agent, catalysts and other additives. Two commonly used isocyanates are TDI (toluene diisocyanate) and MDI (Methylene diphenyl diisocyanate) type isocyanates. Foams made using MDI based isocyanates are known to cure faster, thus resulting in a better density distribution, than foams made using TDI based isocyanates. A higher curing rate is particularly useful in discontinuous foaming processes where higher through put is required and when the foams are high (such as about two meters or higher). However, it is difficult to make low density (for example less than 33 kg/m3) foams with MDI based isocyanates that have acceptable resiliencies and compression sets while also maintaining acceptable tensile strength, elongation to break, and tear strength without the use of any auxiliary blowing agent. There is a tradeoff that is typically observed between the mechanical properties of tensile strength, tear strength, elongation to break on one side with resiliency and compression set on the other side. Furthermore, such low density flexible foams may have uneven density distributions at various heights of the foams.
Therefore, there is a need for low density polyurethane flexible foams which have acceptable density distributions and acceptable balances between the mechanical properties of tensile strength, tear strength, elongation to break on one side with resiliency and compression set on the other side.